1. Field of the Invention
The invention relates to a sheet feeding apparatus for and a sheet feeding method of feeding a sheet to a predetermined position, and a control program for executing a controlling method for the sheet feeding apparatus.
2. Related Background Art
An image forming apparatus such as a color copying machine or a color printer has heretofore been provided with a sheet feeding apparatus for feeding a sheet cut into a predetermined size to a transferring position in order to transfer a toner image formed on a photosensitive member onto the sheet at the transferring position.
As the sheet feeding apparatus, besides one utilizing a frictional roller, there is also, for example, one which air feeds sheets stacked on a stacking tray (see Japanese Patent Application Laid-Open No. S60-082537). According to this apparatus, for example, in order to effect sheet feeding, air is blown against the uppermost portion of the sheets to thereby float up the sheets, and thereafter air suction is effected to thereby suck the uppermost sheet and feed the sheet.
However, depending on the differences in sheet conditions such as the material of the surface of the sheet used, the basis weight of the sheet and the surface smoothness of the sheet, the magnitude of the close contacting force between adjacent sheets in a sheet bundle differs greatly. As this close contacting force between the sheets becomes greater, there occurs a case where it becomes impossible to effect sheet separation by the blowing of the air, and this has led to the problem that the types of actually applicable sheets are restricted to a certain extent.
Such a problem is expected to be further actualized in the future, in color copying machines and color printers as well as offset printing machines, due to the new trend to use sheets of high smoothness such as art paper, coat paper and film to achieve a high quality of image. Particularly under a high-temperature and high-humidity environment, such sheets of high smoothness as mentioned above, because of being very high in the close contacting force between sheets as compared with plain paper, have the possibility that double feed may occur frequently or feeding is not smoothly effected but wrong feeding may occur frequently.
In order to solve these problems, there are known techniques disclosed, for example, Japanese Patent Application Laid-Open No. H07-089625 and Japanese Patent Application Laid-Open No. H10-067442. In Japanese Patent Application Laid-Open No. H07-089625, when air is to be blown against stacked sheets to thereby float the sheets, the uppermost sheet position is detected and on the basis of the result of the position detection, the air discharge amount to be blown is adjusted to thereby control the position of the floated-up sheets.
Also, in Japanese Patent Application Laid-Open No. H10-067442, when air is to be blown against stacked sheets to thereby float up the sheets, the uppermost sheet position is detected and an air nozzle discharging the air is moved to the detected position to thereby control the position of the floated-up sheets.
However, to deter the state of the floated-up sheets within a predetermined range by the use of the aforedescribed technique of the air discharging force control (Japanese Patent Application Laid-Open No. H07-089625) or the air nozzle movement control (Japanese Patent Application Laid-Open No. H10-067442), taking into account the differences in sheet conditions such as the material of the surface of the sheet used, the basis weight of the sheet and the smoothness of the surface of the sheet, there become necessary a hard part which can control an air discharging force or an air nozzle movement amount at high resolving power.
For example, in a case where the rotating speed of a fan motor is minutely changed to thereby realize the control of the air discharging force, there becomes necessary an electric circuit for linearly changing the rotating speed of the fan motor. Particularly, when a very wide range of air discharging force is required, there is the possibility that a plurality of fans conforming to the discharging force must be mounted and one of the plurality of fans must be selected on the basis of the sheet conditions to thereby minutely control the rotating speed of the fan motor.
Also, in a case where an air nozzle moving motor is added to thereby realize the control of the air nozzle movement, there become necessary a mechanical mechanism and a motor driving circuit necessary to move the air nozzle.
In a case where any of these techniques is used, it is impossible to avoid an increase in the cost of the apparatus itself, and this has led to the problem that a sheet feeding apparatus of high performance cannot be realized at a low cost.